O,O-dimethyl S-(N-methylcarbamyl) phosphorodithioate ("dimethoate") is a known pesticide and is available as an emulsifiable concentrate containing an emulsifier and an organic nonaqueous solvent. Consumers dilute the concentrate to form emulsions since the known concentrates are insoluble in water. The resulting mixture is sprayed during agricultural applications.
A pesticidal composition is disclosed in U.S. Pat. No. 3,090,719 that comprises O,O-dimethyldithiophosphorylacetic acid N-monoethylamide, an emulsifier and a solvent that can be cellosolve acetate or a mixture of several other organic solvents such as xylene, primary amyl acetate, carbitol acetate or glycol ether acetate. The patent discloses that it is desirable to exclude solvents containing hydroxy groups to provide more stable compositions.
In U.S. Pat. No. 3,197,362, formulations of O,O-dimethyldithiophosphorylacetic acid N-monoethylamide with a high content of active component and stable at low temperatures are disclosed. The improved characteristics are achieved by use of solvents belonging to the class of aromatic hydrocarbons, aliphatic and cyclic ketones, primary alcohol acetates and glycoethers and trialkylphosphoric esters. Examples of formulations using lower alkyl alcohol solvents are disclosed for comparison purposes.
Liquid anhydrous pesticidal concentrates containing N-methyl-N-formyl amide of O,O-dimethyldithiophosphoryl acetic acid are disclosed in U.S. Pat. No. 3,716,636 wherein the composition is stabilized with an acid anhydride such as acetic anhydride. The composition can also include solvents such as ketones, ethers, esters, hydrocarbons or mixtures thereof. The use of any alcohol as a solvent is not disclosed.
Mixtures of xylene hydrocarbons and cyclohexanone have been used as a solvent system for dimethoate. However, such formulations are unsatisfactory for several reasons. There are limitations to the amount of dimethoate that can be dissolved in cyclohexanone. The most concentrated formulation commercially available at this time contains 4 pounds of dimethoate per gallon of the formulation. Both xylene hydrocarbons and cyclohexanone are toxic materials presenting environmental hazards in production, use and disposal. Known formulations of dimethoate have relatively high freeze points (35.degree.-45.degree. F.) which limit their use in cold weather.
Formation of the emulsions requires the presence of emulsifying agents to create the dispersion of the insoluble concentrate in water. These dispersions are not stable for long periods of time and stratify with different levels of insecticide in the spray mix, possibly resulting in inconsistent spray application. Poor agitation of the diluted spray mix prior to application can result in separation of the dimethoate from the emulsion.
It is the object of this invention to provide a formulation of dimethoate that is water soluble, highly active and tolerant of low temperatures wherein an emulsifier is not required and the solvent system is less toxic to man and animals than solvents used previously.